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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Filesystem-level keyring for fscrypt
4 *
5 * Copyright 2019 Google LLC
6 */
7
8/*
9 * This file implements management of fscrypt master keys in the
10 * filesystem-level keyring, including the ioctls:
11 *
12 * - FS_IOC_ADD_ENCRYPTION_KEY
13 * - FS_IOC_REMOVE_ENCRYPTION_KEY
14 * - FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS
15 * - FS_IOC_GET_ENCRYPTION_KEY_STATUS
16 *
17 * See the "User API" section of Documentation/filesystems/fscrypt.rst for more
18 * information about these ioctls.
19 */
20
21#include <crypto/skcipher.h>
22#include <linux/key-type.h>
23#include <linux/random.h>
24#include <linux/seq_file.h>
25
26#include "fscrypt_private.h"
27
28static void wipe_master_key_secret(struct fscrypt_master_key_secret *secret)
29{
30 fscrypt_destroy_hkdf(&secret->hkdf);
31 memzero_explicit(secret, sizeof(*secret));
32}
33
34static void move_master_key_secret(struct fscrypt_master_key_secret *dst,
35 struct fscrypt_master_key_secret *src)
36{
37 memcpy(dst, src, sizeof(*dst));
38 memzero_explicit(src, sizeof(*src));
39}
40
41static void free_master_key(struct fscrypt_master_key *mk)
42{
43 size_t i;
44
45 wipe_master_key_secret(&mk->mk_secret);
46
47 for (i = 0; i <= __FSCRYPT_MODE_MAX; i++) {
48 fscrypt_destroy_prepared_key(&mk->mk_direct_keys[i]);
49 fscrypt_destroy_prepared_key(&mk->mk_iv_ino_lblk_64_keys[i]);
50 fscrypt_destroy_prepared_key(&mk->mk_iv_ino_lblk_32_keys[i]);
51 }
52
53 key_put(mk->mk_users);
54 kfree_sensitive(mk);
55}
56
57static inline bool valid_key_spec(const struct fscrypt_key_specifier *spec)
58{
59 if (spec->__reserved)
60 return false;
61 return master_key_spec_len(spec) != 0;
62}
63
64static int fscrypt_key_instantiate(struct key *key,
65 struct key_preparsed_payload *prep)
66{
67 key->payload.data[0] = (struct fscrypt_master_key *)prep->data;
68 return 0;
69}
70
71static void fscrypt_key_destroy(struct key *key)
72{
73 free_master_key(key->payload.data[0]);
74}
75
76static void fscrypt_key_describe(const struct key *key, struct seq_file *m)
77{
78 seq_puts(m, key->description);
79
80 if (key_is_positive(key)) {
81 const struct fscrypt_master_key *mk = key->payload.data[0];
82
83 if (!is_master_key_secret_present(&mk->mk_secret))
84 seq_puts(m, ": secret removed");
85 }
86}
87
88/*
89 * Type of key in ->s_master_keys. Each key of this type represents a master
90 * key which has been added to the filesystem. Its payload is a
91 * 'struct fscrypt_master_key'. The "." prefix in the key type name prevents
92 * users from adding keys of this type via the keyrings syscalls rather than via
93 * the intended method of FS_IOC_ADD_ENCRYPTION_KEY.
94 */
95static struct key_type key_type_fscrypt = {
96 .name = "._fscrypt",
97 .instantiate = fscrypt_key_instantiate,
98 .destroy = fscrypt_key_destroy,
99 .describe = fscrypt_key_describe,
100};
101
102static int fscrypt_user_key_instantiate(struct key *key,
103 struct key_preparsed_payload *prep)
104{
105 /*
106 * We just charge FSCRYPT_MAX_KEY_SIZE bytes to the user's key quota for
107 * each key, regardless of the exact key size. The amount of memory
108 * actually used is greater than the size of the raw key anyway.
109 */
110 return key_payload_reserve(key, FSCRYPT_MAX_KEY_SIZE);
111}
112
113static void fscrypt_user_key_describe(const struct key *key, struct seq_file *m)
114{
115 seq_puts(m, key->description);
116}
117
118/*
119 * Type of key in ->mk_users. Each key of this type represents a particular
120 * user who has added a particular master key.
121 *
122 * Note that the name of this key type really should be something like
123 * ".fscrypt-user" instead of simply ".fscrypt". But the shorter name is chosen
124 * mainly for simplicity of presentation in /proc/keys when read by a non-root
125 * user. And it is expected to be rare that a key is actually added by multiple
126 * users, since users should keep their encryption keys confidential.
127 */
128static struct key_type key_type_fscrypt_user = {
129 .name = ".fscrypt",
130 .instantiate = fscrypt_user_key_instantiate,
131 .describe = fscrypt_user_key_describe,
132};
133
134/* Search ->s_master_keys or ->mk_users */
135static struct key *search_fscrypt_keyring(struct key *keyring,
136 struct key_type *type,
137 const char *description)
138{
139 /*
140 * We need to mark the keyring reference as "possessed" so that we
141 * acquire permission to search it, via the KEY_POS_SEARCH permission.
142 */
143 key_ref_t keyref = make_key_ref(keyring, true /* possessed */);
144
145 keyref = keyring_search(keyref, type, description, false);
146 if (IS_ERR(keyref)) {
147 if (PTR_ERR(keyref) == -EAGAIN || /* not found */
148 PTR_ERR(keyref) == -EKEYREVOKED) /* recently invalidated */
149 keyref = ERR_PTR(-ENOKEY);
150 return ERR_CAST(keyref);
151 }
152 return key_ref_to_ptr(keyref);
153}
154
155#define FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE \
156 (CONST_STRLEN("fscrypt-") + sizeof_field(struct super_block, s_id))
157
158#define FSCRYPT_MK_DESCRIPTION_SIZE (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + 1)
159
160#define FSCRYPT_MK_USERS_DESCRIPTION_SIZE \
161 (CONST_STRLEN("fscrypt-") + 2 * FSCRYPT_KEY_IDENTIFIER_SIZE + \
162 CONST_STRLEN("-users") + 1)
163
164#define FSCRYPT_MK_USER_DESCRIPTION_SIZE \
165 (2 * FSCRYPT_KEY_IDENTIFIER_SIZE + CONST_STRLEN(".uid.") + 10 + 1)
166
167static void format_fs_keyring_description(
168 char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE],
169 const struct super_block *sb)
170{
171 sprintf(description, "fscrypt-%s", sb->s_id);
172}
173
174static void format_mk_description(
175 char description[FSCRYPT_MK_DESCRIPTION_SIZE],
176 const struct fscrypt_key_specifier *mk_spec)
177{
178 sprintf(description, "%*phN",
179 master_key_spec_len(mk_spec), (u8 *)&mk_spec->u);
180}
181
182static void format_mk_users_keyring_description(
183 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE],
184 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
185{
186 sprintf(description, "fscrypt-%*phN-users",
187 FSCRYPT_KEY_IDENTIFIER_SIZE, mk_identifier);
188}
189
190static void format_mk_user_description(
191 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE],
192 const u8 mk_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
193{
194
195 sprintf(description, "%*phN.uid.%u", FSCRYPT_KEY_IDENTIFIER_SIZE,
196 mk_identifier, __kuid_val(current_fsuid()));
197}
198
199/* Create ->s_master_keys if needed. Synchronized by fscrypt_add_key_mutex. */
200static int allocate_filesystem_keyring(struct super_block *sb)
201{
202 char description[FSCRYPT_FS_KEYRING_DESCRIPTION_SIZE];
203 struct key *keyring;
204
205 if (sb->s_master_keys)
206 return 0;
207
208 format_fs_keyring_description(description, sb);
209 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
210 current_cred(), KEY_POS_SEARCH |
211 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
212 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
213 if (IS_ERR(keyring))
214 return PTR_ERR(keyring);
215
216 /*
217 * Pairs with the smp_load_acquire() in fscrypt_find_master_key().
218 * I.e., here we publish ->s_master_keys with a RELEASE barrier so that
219 * concurrent tasks can ACQUIRE it.
220 */
221 smp_store_release(&sb->s_master_keys, keyring);
222 return 0;
223}
224
225void fscrypt_sb_free(struct super_block *sb)
226{
227 key_put(sb->s_master_keys);
228 sb->s_master_keys = NULL;
229}
230
231/*
232 * Find the specified master key in ->s_master_keys.
233 * Returns ERR_PTR(-ENOKEY) if not found.
234 */
235struct key *fscrypt_find_master_key(struct super_block *sb,
236 const struct fscrypt_key_specifier *mk_spec)
237{
238 struct key *keyring;
239 char description[FSCRYPT_MK_DESCRIPTION_SIZE];
240
241 /*
242 * Pairs with the smp_store_release() in allocate_filesystem_keyring().
243 * I.e., another task can publish ->s_master_keys concurrently,
244 * executing a RELEASE barrier. We need to use smp_load_acquire() here
245 * to safely ACQUIRE the memory the other task published.
246 */
247 keyring = smp_load_acquire(&sb->s_master_keys);
248 if (keyring == NULL)
249 return ERR_PTR(-ENOKEY); /* No keyring yet, so no keys yet. */
250
251 format_mk_description(description, mk_spec);
252 return search_fscrypt_keyring(keyring, &key_type_fscrypt, description);
253}
254
255static int allocate_master_key_users_keyring(struct fscrypt_master_key *mk)
256{
257 char description[FSCRYPT_MK_USERS_DESCRIPTION_SIZE];
258 struct key *keyring;
259
260 format_mk_users_keyring_description(description,
261 mk->mk_spec.u.identifier);
262 keyring = keyring_alloc(description, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
263 current_cred(), KEY_POS_SEARCH |
264 KEY_USR_SEARCH | KEY_USR_READ | KEY_USR_VIEW,
265 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
266 if (IS_ERR(keyring))
267 return PTR_ERR(keyring);
268
269 mk->mk_users = keyring;
270 return 0;
271}
272
273/*
274 * Find the current user's "key" in the master key's ->mk_users.
275 * Returns ERR_PTR(-ENOKEY) if not found.
276 */
277static struct key *find_master_key_user(struct fscrypt_master_key *mk)
278{
279 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
280
281 format_mk_user_description(description, mk->mk_spec.u.identifier);
282 return search_fscrypt_keyring(mk->mk_users, &key_type_fscrypt_user,
283 description);
284}
285
286/*
287 * Give the current user a "key" in ->mk_users. This charges the user's quota
288 * and marks the master key as added by the current user, so that it cannot be
289 * removed by another user with the key. Either the master key's key->sem must
290 * be held for write, or the master key must be still undergoing initialization.
291 */
292static int add_master_key_user(struct fscrypt_master_key *mk)
293{
294 char description[FSCRYPT_MK_USER_DESCRIPTION_SIZE];
295 struct key *mk_user;
296 int err;
297
298 format_mk_user_description(description, mk->mk_spec.u.identifier);
299 mk_user = key_alloc(&key_type_fscrypt_user, description,
300 current_fsuid(), current_gid(), current_cred(),
301 KEY_POS_SEARCH | KEY_USR_VIEW, 0, NULL);
302 if (IS_ERR(mk_user))
303 return PTR_ERR(mk_user);
304
305 err = key_instantiate_and_link(mk_user, NULL, 0, mk->mk_users, NULL);
306 key_put(mk_user);
307 return err;
308}
309
310/*
311 * Remove the current user's "key" from ->mk_users.
312 * The master key's key->sem must be held for write.
313 *
314 * Returns 0 if removed, -ENOKEY if not found, or another -errno code.
315 */
316static int remove_master_key_user(struct fscrypt_master_key *mk)
317{
318 struct key *mk_user;
319 int err;
320
321 mk_user = find_master_key_user(mk);
322 if (IS_ERR(mk_user))
323 return PTR_ERR(mk_user);
324 err = key_unlink(mk->mk_users, mk_user);
325 key_put(mk_user);
326 return err;
327}
328
329/*
330 * Allocate a new fscrypt_master_key which contains the given secret, set it as
331 * the payload of a new 'struct key' of type fscrypt, and link the 'struct key'
332 * into the given keyring. Synchronized by fscrypt_add_key_mutex.
333 */
334static int add_new_master_key(struct fscrypt_master_key_secret *secret,
335 const struct fscrypt_key_specifier *mk_spec,
336 struct key *keyring)
337{
338 struct fscrypt_master_key *mk;
339 char description[FSCRYPT_MK_DESCRIPTION_SIZE];
340 struct key *key;
341 int err;
342
343 mk = kzalloc(sizeof(*mk), GFP_KERNEL);
344 if (!mk)
345 return -ENOMEM;
346
347 mk->mk_spec = *mk_spec;
348
349 move_master_key_secret(&mk->mk_secret, secret);
350 init_rwsem(&mk->mk_secret_sem);
351
352 refcount_set(&mk->mk_refcount, 1); /* secret is present */
353 INIT_LIST_HEAD(&mk->mk_decrypted_inodes);
354 spin_lock_init(&mk->mk_decrypted_inodes_lock);
355
356 if (mk_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
357 err = allocate_master_key_users_keyring(mk);
358 if (err)
359 goto out_free_mk;
360 err = add_master_key_user(mk);
361 if (err)
362 goto out_free_mk;
363 }
364
365 /*
366 * Note that we don't charge this key to anyone's quota, since when
367 * ->mk_users is in use those keys are charged instead, and otherwise
368 * (when ->mk_users isn't in use) only root can add these keys.
369 */
370 format_mk_description(description, mk_spec);
371 key = key_alloc(&key_type_fscrypt, description,
372 GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, current_cred(),
373 KEY_POS_SEARCH | KEY_USR_SEARCH | KEY_USR_VIEW,
374 KEY_ALLOC_NOT_IN_QUOTA, NULL);
375 if (IS_ERR(key)) {
376 err = PTR_ERR(key);
377 goto out_free_mk;
378 }
379 err = key_instantiate_and_link(key, mk, sizeof(*mk), keyring, NULL);
380 key_put(key);
381 if (err)
382 goto out_free_mk;
383
384 return 0;
385
386out_free_mk:
387 free_master_key(mk);
388 return err;
389}
390
391#define KEY_DEAD 1
392
393static int add_existing_master_key(struct fscrypt_master_key *mk,
394 struct fscrypt_master_key_secret *secret)
395{
396 struct key *mk_user;
397 bool rekey;
398 int err;
399
400 /*
401 * If the current user is already in ->mk_users, then there's nothing to
402 * do. (Not applicable for v1 policy keys, which have NULL ->mk_users.)
403 */
404 if (mk->mk_users) {
405 mk_user = find_master_key_user(mk);
406 if (mk_user != ERR_PTR(-ENOKEY)) {
407 if (IS_ERR(mk_user))
408 return PTR_ERR(mk_user);
409 key_put(mk_user);
410 return 0;
411 }
412 }
413
414 /* If we'll be re-adding ->mk_secret, try to take the reference. */
415 rekey = !is_master_key_secret_present(&mk->mk_secret);
416 if (rekey && !refcount_inc_not_zero(&mk->mk_refcount))
417 return KEY_DEAD;
418
419 /* Add the current user to ->mk_users, if applicable. */
420 if (mk->mk_users) {
421 err = add_master_key_user(mk);
422 if (err) {
423 if (rekey && refcount_dec_and_test(&mk->mk_refcount))
424 return KEY_DEAD;
425 return err;
426 }
427 }
428
429 /* Re-add the secret if needed. */
430 if (rekey) {
431 down_write(&mk->mk_secret_sem);
432 move_master_key_secret(&mk->mk_secret, secret);
433 up_write(&mk->mk_secret_sem);
434 }
435 return 0;
436}
437
438static int do_add_master_key(struct super_block *sb,
439 struct fscrypt_master_key_secret *secret,
440 const struct fscrypt_key_specifier *mk_spec)
441{
442 static DEFINE_MUTEX(fscrypt_add_key_mutex);
443 struct key *key;
444 int err;
445
446 mutex_lock(&fscrypt_add_key_mutex); /* serialize find + link */
447retry:
448 key = fscrypt_find_master_key(sb, mk_spec);
449 if (IS_ERR(key)) {
450 err = PTR_ERR(key);
451 if (err != -ENOKEY)
452 goto out_unlock;
453 /* Didn't find the key in ->s_master_keys. Add it. */
454 err = allocate_filesystem_keyring(sb);
455 if (err)
456 goto out_unlock;
457 err = add_new_master_key(secret, mk_spec, sb->s_master_keys);
458 } else {
459 /*
460 * Found the key in ->s_master_keys. Re-add the secret if
461 * needed, and add the user to ->mk_users if needed.
462 */
463 down_write(&key->sem);
464 err = add_existing_master_key(key->payload.data[0], secret);
465 up_write(&key->sem);
466 if (err == KEY_DEAD) {
467 /* Key being removed or needs to be removed */
468 key_invalidate(key);
469 key_put(key);
470 goto retry;
471 }
472 key_put(key);
473 }
474out_unlock:
475 mutex_unlock(&fscrypt_add_key_mutex);
476 return err;
477}
478
479static int add_master_key(struct super_block *sb,
480 struct fscrypt_master_key_secret *secret,
481 struct fscrypt_key_specifier *key_spec)
482{
483 int err;
484
485 if (key_spec->type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER) {
486 err = fscrypt_init_hkdf(&secret->hkdf, secret->raw,
487 secret->size);
488 if (err)
489 return err;
490
491 /*
492 * Now that the HKDF context is initialized, the raw key is no
493 * longer needed.
494 */
495 memzero_explicit(secret->raw, secret->size);
496
497 /* Calculate the key identifier */
498 err = fscrypt_hkdf_expand(&secret->hkdf,
499 HKDF_CONTEXT_KEY_IDENTIFIER, NULL, 0,
500 key_spec->u.identifier,
501 FSCRYPT_KEY_IDENTIFIER_SIZE);
502 if (err)
503 return err;
504 }
505 return do_add_master_key(sb, secret, key_spec);
506}
507
508static int fscrypt_provisioning_key_preparse(struct key_preparsed_payload *prep)
509{
510 const struct fscrypt_provisioning_key_payload *payload = prep->data;
511
512 if (prep->datalen < sizeof(*payload) + FSCRYPT_MIN_KEY_SIZE ||
513 prep->datalen > sizeof(*payload) + FSCRYPT_MAX_KEY_SIZE)
514 return -EINVAL;
515
516 if (payload->type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
517 payload->type != FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER)
518 return -EINVAL;
519
520 if (payload->__reserved)
521 return -EINVAL;
522
523 prep->payload.data[0] = kmemdup(payload, prep->datalen, GFP_KERNEL);
524 if (!prep->payload.data[0])
525 return -ENOMEM;
526
527 prep->quotalen = prep->datalen;
528 return 0;
529}
530
531static void fscrypt_provisioning_key_free_preparse(
532 struct key_preparsed_payload *prep)
533{
534 kfree_sensitive(prep->payload.data[0]);
535}
536
537static void fscrypt_provisioning_key_describe(const struct key *key,
538 struct seq_file *m)
539{
540 seq_puts(m, key->description);
541 if (key_is_positive(key)) {
542 const struct fscrypt_provisioning_key_payload *payload =
543 key->payload.data[0];
544
545 seq_printf(m, ": %u [%u]", key->datalen, payload->type);
546 }
547}
548
549static void fscrypt_provisioning_key_destroy(struct key *key)
550{
551 kfree_sensitive(key->payload.data[0]);
552}
553
554static struct key_type key_type_fscrypt_provisioning = {
555 .name = "fscrypt-provisioning",
556 .preparse = fscrypt_provisioning_key_preparse,
557 .free_preparse = fscrypt_provisioning_key_free_preparse,
558 .instantiate = generic_key_instantiate,
559 .describe = fscrypt_provisioning_key_describe,
560 .destroy = fscrypt_provisioning_key_destroy,
561};
562
563/*
564 * Retrieve the raw key from the Linux keyring key specified by 'key_id', and
565 * store it into 'secret'.
566 *
567 * The key must be of type "fscrypt-provisioning" and must have the field
568 * fscrypt_provisioning_key_payload::type set to 'type', indicating that it's
569 * only usable with fscrypt with the particular KDF version identified by
570 * 'type'. We don't use the "logon" key type because there's no way to
571 * completely restrict the use of such keys; they can be used by any kernel API
572 * that accepts "logon" keys and doesn't require a specific service prefix.
573 *
574 * The ability to specify the key via Linux keyring key is intended for cases
575 * where userspace needs to re-add keys after the filesystem is unmounted and
576 * re-mounted. Most users should just provide the raw key directly instead.
577 */
578static int get_keyring_key(u32 key_id, u32 type,
579 struct fscrypt_master_key_secret *secret)
580{
581 key_ref_t ref;
582 struct key *key;
583 const struct fscrypt_provisioning_key_payload *payload;
584 int err;
585
586 ref = lookup_user_key(key_id, 0, KEY_NEED_SEARCH);
587 if (IS_ERR(ref))
588 return PTR_ERR(ref);
589 key = key_ref_to_ptr(ref);
590
591 if (key->type != &key_type_fscrypt_provisioning)
592 goto bad_key;
593 payload = key->payload.data[0];
594
595 /* Don't allow fscrypt v1 keys to be used as v2 keys and vice versa. */
596 if (payload->type != type)
597 goto bad_key;
598
599 secret->size = key->datalen - sizeof(*payload);
600 memcpy(secret->raw, payload->raw, secret->size);
601 err = 0;
602 goto out_put;
603
604bad_key:
605 err = -EKEYREJECTED;
606out_put:
607 key_ref_put(ref);
608 return err;
609}
610
611/*
612 * Add a master encryption key to the filesystem, causing all files which were
613 * encrypted with it to appear "unlocked" (decrypted) when accessed.
614 *
615 * When adding a key for use by v1 encryption policies, this ioctl is
616 * privileged, and userspace must provide the 'key_descriptor'.
617 *
618 * When adding a key for use by v2+ encryption policies, this ioctl is
619 * unprivileged. This is needed, in general, to allow non-root users to use
620 * encryption without encountering the visibility problems of process-subscribed
621 * keyrings and the inability to properly remove keys. This works by having
622 * each key identified by its cryptographically secure hash --- the
623 * 'key_identifier'. The cryptographic hash ensures that a malicious user
624 * cannot add the wrong key for a given identifier. Furthermore, each added key
625 * is charged to the appropriate user's quota for the keyrings service, which
626 * prevents a malicious user from adding too many keys. Finally, we forbid a
627 * user from removing a key while other users have added it too, which prevents
628 * a user who knows another user's key from causing a denial-of-service by
629 * removing it at an inopportune time. (We tolerate that a user who knows a key
630 * can prevent other users from removing it.)
631 *
632 * For more details, see the "FS_IOC_ADD_ENCRYPTION_KEY" section of
633 * Documentation/filesystems/fscrypt.rst.
634 */
635int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
636{
637 struct super_block *sb = file_inode(filp)->i_sb;
638 struct fscrypt_add_key_arg __user *uarg = _uarg;
639 struct fscrypt_add_key_arg arg;
640 struct fscrypt_master_key_secret secret;
641 int err;
642
643 if (copy_from_user(&arg, uarg, sizeof(arg)))
644 return -EFAULT;
645
646 if (!valid_key_spec(&arg.key_spec))
647 return -EINVAL;
648
649 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
650 return -EINVAL;
651
652 /*
653 * Only root can add keys that are identified by an arbitrary descriptor
654 * rather than by a cryptographic hash --- since otherwise a malicious
655 * user could add the wrong key.
656 */
657 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
658 !capable(CAP_SYS_ADMIN))
659 return -EACCES;
660
661 memset(&secret, 0, sizeof(secret));
662 if (arg.key_id) {
663 if (arg.raw_size != 0)
664 return -EINVAL;
665 err = get_keyring_key(arg.key_id, arg.key_spec.type, &secret);
666 if (err)
667 goto out_wipe_secret;
668 } else {
669 if (arg.raw_size < FSCRYPT_MIN_KEY_SIZE ||
670 arg.raw_size > FSCRYPT_MAX_KEY_SIZE)
671 return -EINVAL;
672 secret.size = arg.raw_size;
673 err = -EFAULT;
674 if (copy_from_user(secret.raw, uarg->raw, secret.size))
675 goto out_wipe_secret;
676 }
677
678 err = add_master_key(sb, &secret, &arg.key_spec);
679 if (err)
680 goto out_wipe_secret;
681
682 /* Return the key identifier to userspace, if applicable */
683 err = -EFAULT;
684 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER &&
685 copy_to_user(uarg->key_spec.u.identifier, arg.key_spec.u.identifier,
686 FSCRYPT_KEY_IDENTIFIER_SIZE))
687 goto out_wipe_secret;
688 err = 0;
689out_wipe_secret:
690 wipe_master_key_secret(&secret);
691 return err;
692}
693EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
694
695/*
696 * Add the key for '-o test_dummy_encryption' to the filesystem keyring.
697 *
698 * Use a per-boot random key to prevent people from misusing this option.
699 */
700int fscrypt_add_test_dummy_key(struct super_block *sb,
701 struct fscrypt_key_specifier *key_spec)
702{
703 static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
704 struct fscrypt_master_key_secret secret;
705 int err;
706
707 get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
708
709 memset(&secret, 0, sizeof(secret));
710 secret.size = FSCRYPT_MAX_KEY_SIZE;
711 memcpy(secret.raw, test_key, FSCRYPT_MAX_KEY_SIZE);
712
713 err = add_master_key(sb, &secret, key_spec);
714 wipe_master_key_secret(&secret);
715 return err;
716}
717
718/*
719 * Verify that the current user has added a master key with the given identifier
720 * (returns -ENOKEY if not). This is needed to prevent a user from encrypting
721 * their files using some other user's key which they don't actually know.
722 * Cryptographically this isn't much of a problem, but the semantics of this
723 * would be a bit weird, so it's best to just forbid it.
724 *
725 * The system administrator (CAP_FOWNER) can override this, which should be
726 * enough for any use cases where encryption policies are being set using keys
727 * that were chosen ahead of time but aren't available at the moment.
728 *
729 * Note that the key may have already removed by the time this returns, but
730 * that's okay; we just care whether the key was there at some point.
731 *
732 * Return: 0 if the key is added, -ENOKEY if it isn't, or another -errno code
733 */
734int fscrypt_verify_key_added(struct super_block *sb,
735 const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
736{
737 struct fscrypt_key_specifier mk_spec;
738 struct key *key, *mk_user;
739 struct fscrypt_master_key *mk;
740 int err;
741
742 mk_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
743 memcpy(mk_spec.u.identifier, identifier, FSCRYPT_KEY_IDENTIFIER_SIZE);
744
745 key = fscrypt_find_master_key(sb, &mk_spec);
746 if (IS_ERR(key)) {
747 err = PTR_ERR(key);
748 goto out;
749 }
750 mk = key->payload.data[0];
751 mk_user = find_master_key_user(mk);
752 if (IS_ERR(mk_user)) {
753 err = PTR_ERR(mk_user);
754 } else {
755 key_put(mk_user);
756 err = 0;
757 }
758 key_put(key);
759out:
760 if (err == -ENOKEY && capable(CAP_FOWNER))
761 err = 0;
762 return err;
763}
764
765/*
766 * Try to evict the inode's dentries from the dentry cache. If the inode is a
767 * directory, then it can have at most one dentry; however, that dentry may be
768 * pinned by child dentries, so first try to evict the children too.
769 */
770static void shrink_dcache_inode(struct inode *inode)
771{
772 struct dentry *dentry;
773
774 if (S_ISDIR(inode->i_mode)) {
775 dentry = d_find_any_alias(inode);
776 if (dentry) {
777 shrink_dcache_parent(dentry);
778 dput(dentry);
779 }
780 }
781 d_prune_aliases(inode);
782}
783
784static void evict_dentries_for_decrypted_inodes(struct fscrypt_master_key *mk)
785{
786 struct fscrypt_info *ci;
787 struct inode *inode;
788 struct inode *toput_inode = NULL;
789
790 spin_lock(&mk->mk_decrypted_inodes_lock);
791
792 list_for_each_entry(ci, &mk->mk_decrypted_inodes, ci_master_key_link) {
793 inode = ci->ci_inode;
794 spin_lock(&inode->i_lock);
795 if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
796 spin_unlock(&inode->i_lock);
797 continue;
798 }
799 __iget(inode);
800 spin_unlock(&inode->i_lock);
801 spin_unlock(&mk->mk_decrypted_inodes_lock);
802
803 shrink_dcache_inode(inode);
804 iput(toput_inode);
805 toput_inode = inode;
806
807 spin_lock(&mk->mk_decrypted_inodes_lock);
808 }
809
810 spin_unlock(&mk->mk_decrypted_inodes_lock);
811 iput(toput_inode);
812}
813
814static int check_for_busy_inodes(struct super_block *sb,
815 struct fscrypt_master_key *mk)
816{
817 struct list_head *pos;
818 size_t busy_count = 0;
819 unsigned long ino;
820
821 spin_lock(&mk->mk_decrypted_inodes_lock);
822
823 list_for_each(pos, &mk->mk_decrypted_inodes)
824 busy_count++;
825
826 if (busy_count == 0) {
827 spin_unlock(&mk->mk_decrypted_inodes_lock);
828 return 0;
829 }
830
831 {
832 /* select an example file to show for debugging purposes */
833 struct inode *inode =
834 list_first_entry(&mk->mk_decrypted_inodes,
835 struct fscrypt_info,
836 ci_master_key_link)->ci_inode;
837 ino = inode->i_ino;
838 }
839 spin_unlock(&mk->mk_decrypted_inodes_lock);
840
841 fscrypt_warn(NULL,
842 "%s: %zu inode(s) still busy after removing key with %s %*phN, including ino %lu",
843 sb->s_id, busy_count, master_key_spec_type(&mk->mk_spec),
844 master_key_spec_len(&mk->mk_spec), (u8 *)&mk->mk_spec.u,
845 ino);
846 return -EBUSY;
847}
848
849static int try_to_lock_encrypted_files(struct super_block *sb,
850 struct fscrypt_master_key *mk)
851{
852 int err1;
853 int err2;
854
855 /*
856 * An inode can't be evicted while it is dirty or has dirty pages.
857 * Thus, we first have to clean the inodes in ->mk_decrypted_inodes.
858 *
859 * Just do it the easy way: call sync_filesystem(). It's overkill, but
860 * it works, and it's more important to minimize the amount of caches we
861 * drop than the amount of data we sync. Also, unprivileged users can
862 * already call sync_filesystem() via sys_syncfs() or sys_sync().
863 */
864 down_read(&sb->s_umount);
865 err1 = sync_filesystem(sb);
866 up_read(&sb->s_umount);
867 /* If a sync error occurs, still try to evict as much as possible. */
868
869 /*
870 * Inodes are pinned by their dentries, so we have to evict their
871 * dentries. shrink_dcache_sb() would suffice, but would be overkill
872 * and inappropriate for use by unprivileged users. So instead go
873 * through the inodes' alias lists and try to evict each dentry.
874 */
875 evict_dentries_for_decrypted_inodes(mk);
876
877 /*
878 * evict_dentries_for_decrypted_inodes() already iput() each inode in
879 * the list; any inodes for which that dropped the last reference will
880 * have been evicted due to fscrypt_drop_inode() detecting the key
881 * removal and telling the VFS to evict the inode. So to finish, we
882 * just need to check whether any inodes couldn't be evicted.
883 */
884 err2 = check_for_busy_inodes(sb, mk);
885
886 return err1 ?: err2;
887}
888
889/*
890 * Try to remove an fscrypt master encryption key.
891 *
892 * FS_IOC_REMOVE_ENCRYPTION_KEY (all_users=false) removes the current user's
893 * claim to the key, then removes the key itself if no other users have claims.
894 * FS_IOC_REMOVE_ENCRYPTION_KEY_ALL_USERS (all_users=true) always removes the
895 * key itself.
896 *
897 * To "remove the key itself", first we wipe the actual master key secret, so
898 * that no more inodes can be unlocked with it. Then we try to evict all cached
899 * inodes that had been unlocked with the key.
900 *
901 * If all inodes were evicted, then we unlink the fscrypt_master_key from the
902 * keyring. Otherwise it remains in the keyring in the "incompletely removed"
903 * state (without the actual secret key) where it tracks the list of remaining
904 * inodes. Userspace can execute the ioctl again later to retry eviction, or
905 * alternatively can re-add the secret key again.
906 *
907 * For more details, see the "Removing keys" section of
908 * Documentation/filesystems/fscrypt.rst.
909 */
910static int do_remove_key(struct file *filp, void __user *_uarg, bool all_users)
911{
912 struct super_block *sb = file_inode(filp)->i_sb;
913 struct fscrypt_remove_key_arg __user *uarg = _uarg;
914 struct fscrypt_remove_key_arg arg;
915 struct key *key;
916 struct fscrypt_master_key *mk;
917 u32 status_flags = 0;
918 int err;
919 bool dead;
920
921 if (copy_from_user(&arg, uarg, sizeof(arg)))
922 return -EFAULT;
923
924 if (!valid_key_spec(&arg.key_spec))
925 return -EINVAL;
926
927 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
928 return -EINVAL;
929
930 /*
931 * Only root can add and remove keys that are identified by an arbitrary
932 * descriptor rather than by a cryptographic hash.
933 */
934 if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR &&
935 !capable(CAP_SYS_ADMIN))
936 return -EACCES;
937
938 /* Find the key being removed. */
939 key = fscrypt_find_master_key(sb, &arg.key_spec);
940 if (IS_ERR(key))
941 return PTR_ERR(key);
942 mk = key->payload.data[0];
943
944 down_write(&key->sem);
945
946 /* If relevant, remove current user's (or all users) claim to the key */
947 if (mk->mk_users && mk->mk_users->keys.nr_leaves_on_tree != 0) {
948 if (all_users)
949 err = keyring_clear(mk->mk_users);
950 else
951 err = remove_master_key_user(mk);
952 if (err) {
953 up_write(&key->sem);
954 goto out_put_key;
955 }
956 if (mk->mk_users->keys.nr_leaves_on_tree != 0) {
957 /*
958 * Other users have still added the key too. We removed
959 * the current user's claim to the key, but we still
960 * can't remove the key itself.
961 */
962 status_flags |=
963 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_OTHER_USERS;
964 err = 0;
965 up_write(&key->sem);
966 goto out_put_key;
967 }
968 }
969
970 /* No user claims remaining. Go ahead and wipe the secret. */
971 dead = false;
972 if (is_master_key_secret_present(&mk->mk_secret)) {
973 down_write(&mk->mk_secret_sem);
974 wipe_master_key_secret(&mk->mk_secret);
975 dead = refcount_dec_and_test(&mk->mk_refcount);
976 up_write(&mk->mk_secret_sem);
977 }
978 up_write(&key->sem);
979 if (dead) {
980 /*
981 * No inodes reference the key, and we wiped the secret, so the
982 * key object is free to be removed from the keyring.
983 */
984 key_invalidate(key);
985 err = 0;
986 } else {
987 /* Some inodes still reference this key; try to evict them. */
988 err = try_to_lock_encrypted_files(sb, mk);
989 if (err == -EBUSY) {
990 status_flags |=
991 FSCRYPT_KEY_REMOVAL_STATUS_FLAG_FILES_BUSY;
992 err = 0;
993 }
994 }
995 /*
996 * We return 0 if we successfully did something: removed a claim to the
997 * key, wiped the secret, or tried locking the files again. Users need
998 * to check the informational status flags if they care whether the key
999 * has been fully removed including all files locked.
1000 */
1001out_put_key:
1002 key_put(key);
1003 if (err == 0)
1004 err = put_user(status_flags, &uarg->removal_status_flags);
1005 return err;
1006}
1007
1008int fscrypt_ioctl_remove_key(struct file *filp, void __user *uarg)
1009{
1010 return do_remove_key(filp, uarg, false);
1011}
1012EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key);
1013
1014int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *uarg)
1015{
1016 if (!capable(CAP_SYS_ADMIN))
1017 return -EACCES;
1018 return do_remove_key(filp, uarg, true);
1019}
1020EXPORT_SYMBOL_GPL(fscrypt_ioctl_remove_key_all_users);
1021
1022/*
1023 * Retrieve the status of an fscrypt master encryption key.
1024 *
1025 * We set ->status to indicate whether the key is absent, present, or
1026 * incompletely removed. "Incompletely removed" means that the master key
1027 * secret has been removed, but some files which had been unlocked with it are
1028 * still in use. This field allows applications to easily determine the state
1029 * of an encrypted directory without using a hack such as trying to open a
1030 * regular file in it (which can confuse the "incompletely removed" state with
1031 * absent or present).
1032 *
1033 * In addition, for v2 policy keys we allow applications to determine, via
1034 * ->status_flags and ->user_count, whether the key has been added by the
1035 * current user, by other users, or by both. Most applications should not need
1036 * this, since ordinarily only one user should know a given key. However, if a
1037 * secret key is shared by multiple users, applications may wish to add an
1038 * already-present key to prevent other users from removing it. This ioctl can
1039 * be used to check whether that really is the case before the work is done to
1040 * add the key --- which might e.g. require prompting the user for a passphrase.
1041 *
1042 * For more details, see the "FS_IOC_GET_ENCRYPTION_KEY_STATUS" section of
1043 * Documentation/filesystems/fscrypt.rst.
1044 */
1045int fscrypt_ioctl_get_key_status(struct file *filp, void __user *uarg)
1046{
1047 struct super_block *sb = file_inode(filp)->i_sb;
1048 struct fscrypt_get_key_status_arg arg;
1049 struct key *key;
1050 struct fscrypt_master_key *mk;
1051 int err;
1052
1053 if (copy_from_user(&arg, uarg, sizeof(arg)))
1054 return -EFAULT;
1055
1056 if (!valid_key_spec(&arg.key_spec))
1057 return -EINVAL;
1058
1059 if (memchr_inv(arg.__reserved, 0, sizeof(arg.__reserved)))
1060 return -EINVAL;
1061
1062 arg.status_flags = 0;
1063 arg.user_count = 0;
1064 memset(arg.__out_reserved, 0, sizeof(arg.__out_reserved));
1065
1066 key = fscrypt_find_master_key(sb, &arg.key_spec);
1067 if (IS_ERR(key)) {
1068 if (key != ERR_PTR(-ENOKEY))
1069 return PTR_ERR(key);
1070 arg.status = FSCRYPT_KEY_STATUS_ABSENT;
1071 err = 0;
1072 goto out;
1073 }
1074 mk = key->payload.data[0];
1075 down_read(&key->sem);
1076
1077 if (!is_master_key_secret_present(&mk->mk_secret)) {
1078 arg.status = FSCRYPT_KEY_STATUS_INCOMPLETELY_REMOVED;
1079 err = 0;
1080 goto out_release_key;
1081 }
1082
1083 arg.status = FSCRYPT_KEY_STATUS_PRESENT;
1084 if (mk->mk_users) {
1085 struct key *mk_user;
1086
1087 arg.user_count = mk->mk_users->keys.nr_leaves_on_tree;
1088 mk_user = find_master_key_user(mk);
1089 if (!IS_ERR(mk_user)) {
1090 arg.status_flags |=
1091 FSCRYPT_KEY_STATUS_FLAG_ADDED_BY_SELF;
1092 key_put(mk_user);
1093 } else if (mk_user != ERR_PTR(-ENOKEY)) {
1094 err = PTR_ERR(mk_user);
1095 goto out_release_key;
1096 }
1097 }
1098 err = 0;
1099out_release_key:
1100 up_read(&key->sem);
1101 key_put(key);
1102out:
1103 if (!err && copy_to_user(uarg, &arg, sizeof(arg)))
1104 err = -EFAULT;
1105 return err;
1106}
1107EXPORT_SYMBOL_GPL(fscrypt_ioctl_get_key_status);
1108
1109int __init fscrypt_init_keyring(void)
1110{
1111 int err;
1112
1113 err = register_key_type(&key_type_fscrypt);
1114 if (err)
1115 return err;
1116
1117 err = register_key_type(&key_type_fscrypt_user);
1118 if (err)
1119 goto err_unregister_fscrypt;
1120
1121 err = register_key_type(&key_type_fscrypt_provisioning);
1122 if (err)
1123 goto err_unregister_fscrypt_user;
1124
1125 return 0;
1126
1127err_unregister_fscrypt_user:
1128 unregister_key_type(&key_type_fscrypt_user);
1129err_unregister_fscrypt:
1130 unregister_key_type(&key_type_fscrypt);
1131 return err;
1132}